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A Correction Method for Stationary Fan CFD MRF Models 2009-01-0178

A common fan model to use in automotive under hood simulations is the Multiple Reference Frame (MRF) model and within the industry, for this specific application, this model is well known to under predict performance.

In this paper we have examined the possibilities of correcting this deficiency with a simple “speed correction”. This is done by testing and simulating a production fan in the Volvo Fan Test Rig for two operating speeds, 1200 rpm and 2400 rpm. Pressure rise, fan power and static efficiency are presented as functions of volumetric flow rate. The simulations verify that using the MRF model the common behavior of under predicting pressure rise and performance of the fan occur. In addition, this work shows that; although the MRF is not predicting fan performance correctly it constitutes a reliable fan modeling strategy. In fact, the classical fan laws apply to the MRF model, and this justifies the suggested procedure of simply “speed correcting” the fan and by doing so a consistent behavior is received. For a standard 750 mm production fan, it is shown that by increasing the fan speed with 14%, throughout the range of operating speeds, one accurately models the pressure rise over mass flow for most of vehicle operating conditions.